Finding the Last Photo Taken

Getting the last photo taken is a convenient feature to have in your app when dealing with photo picking. Prior to iOS 8, you could get it by using the Assets Library Framework and then looping through the various groups to get the right photo.

In iOS 8, the Asset Library is still available, but Apple introduced a new framework to go along with Photos.app. It’s creatively called the Photos Framework and it makes certain things, such as querying for the recent image much easier. To further entice you to use it, the Assets Library is deprecated in iOS 9.

Here’s a function that’ll get the most recent photo with the Photos Framework:

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import UIKit
import Photos

// I like to typealias my blocks, makes for easier reading
typealias ImageCallback = (UIImage? -> Void)

func fetchLastPhoto(resizeTo size: CGSize?, imageCallback: ImageCallback) {
    let fetchOptions = PHFetchOptions()
    fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]

//        fetchOptions.fetchLimit = 1 // Available in iOS 9

    if let fetchResult = PHAsset.fetchAssetsWithMediaType(.Image, options: fetchOptions) {
        if let asset = fetchResult.firstObject as? PHAsset {
            let manager = PHImageManager.defaultManager()
            let targetSize = size == nil ? CGSize(width: asset.pixelWidth, height: asset.pixelHeight) : size!
            manager.requestImageForAsset(asset,
                targetSize: targetSize,
                contentMode: .AspectFit,
                options: nil,
                resultHandler: { image, info in
                imageCallback(image)
            })
        } else {
            imageCallback(nil)
        }
    }
}

There’s a fair amount going on in there. First, we create a PHFetchOptions object which we can use to pass in additional information to filter the query. In this case we only need to sort by creationDate descending. iOS 9 introduces fetchLimit which could reduce a bit of overhead since we know we only need 1 image.

PHFetchOptions also has a predicate property that has a bunch of interesting capabilities, such as restricting the search to specific mediaSubtypes like PhotoHDR or PhotoPanorama. If you want all photos just ignore it; that’s determined later. Do note that “Photos does not support predicates created with the predicateWithBlock: method.”.

Once we have our options we are ready to query. The Photos Framework gives you access to 3 types of things that are stored in Photos.app: PHAsset, PHAssetCollection, and PHCollectionList. We only care about PHAsset right now. A PHAsset is a representation of the media stored on the device (photo or video). The other two are ways to group those assets in general.

Querying happens through class-level methods on the PHAsset class. There are a few to choose from, but we want fetchAssetsWithMediaType:options:. This returns a PHFetchResult which is kinda like an NSArray, but not exactly. In Swift it’s filled with optional AnyObjects. The first one should be the most recently created file so we cast it to a PHAsset.

Now comes the time to convert that PHAsset into what we really want: a UIImage. This is the responsibility of PHImageManager.

Most of the time when querying for images, we just want to resize the photo to fit into a UIImageView so Photos does most of the heavy lifting for you. Give it the size you want and a couple other options and off it will go. This happens asynchronously, so hand off the results to your callback block when it’s done. This’d be especially handy for generating a bunch of thumbnails.

Photos gives you quite a bit of flexability. We didn’t touch on how it helps you to edit assets, manage/query video, or observe changes to photos. I wasn’t aware of this framework until today, but it looks like a powerful one worth getting to know if you do anything with the images on your device.

Tags: code

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